Isotopic evidence for the formation of the moon in a canonical giant impact

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nielsen, S. G., Bekaert, D. V., & Auro, M. Isotopic evidence for the formation of the moon in a canonical giant impact. Nature Communications, 12(1), (2021): 1817, https://doi.org/10.1038/s41467-021-22155-7.Isotopic measurements of lunar and terrestrial rocks have revealed that, unlike any other body in the solar system, the Moon is indistinguishable from the Earth for nearly every isotopic system. This observation, however, contradicts predictions by the standard model for the origin of the Moon, the canonical giant impact. Here we show that the vanadium isotopic composition of the Moon is offset from that of the bulk silicate Earth by 0.18 ± 0.04 parts per thousand towards the chondritic value. This offset most likely results from isotope fractionation on proto-Earth during the main stage of terrestrial core formation (pre-giant impact), followed by a canonical giant impact where ~80% of the Moon originates from the impactor of chondritic composition. Our data refute the possibility of post-giant impact equilibration between the Earth and Moon, and implies that the impactor and proto-Earth mainly accreted from a common isotopic reservoir in the inner solar system.This study was funded by NASA Emerging Worlds grant NNX16AD36G to S.G.N. We thank NASA-JSC, Tony Irving, and Thorsten Kleine for access to meteorite and Apollo mission samples. US Antarctic meteorite samples are recovered by the Antarctic Search for Meteorites (ANSMET) program, which has been funded by NSF and NASA, and characterized and curated by the Astromaterials Curation Office at NASA Johnson Space Center and the Department of Mineral Sciences of the Smithsonian Institution. J. Blusztajn is thanked for help with mass spectrometry support at WHOI

Improvements to 232-thorium, 230-thorium, and 231-protactinium analysis in seawater arising from GEOTRACES intercalibration

The GEOTRACES program requires the analysis of large numbers of seawater samples for ^(232)Th, ^(230)Th, and ^(231)Pa. During the GEOTRACES international intercalibration exercise, we encountered unexpected difficulties with recovery and contamination of these isotopes, ^(232)Th in particular. Experiments were carried out to identify the source of these issues, leading to a more streamlined and efficient procedure. The two particular problems that we identified and corrected were (1) frits in columns supplied by Bio-Rad Laboratories caused loss of Th during column chemistry and (2) new batches of AG1-X8 resin supplied by Bio-Rad Laboratories released more than 100 pg of ^(232)Th during elution of sample. To improve yields and blanks, we implemented a series of changes including switching to Eichrom anion exchange resin (100-200 μm mesh) and Environmental Express columns. All Th and Pa samples were analyzed on a Neptune multi-collector inductively-coupled-plasma mass spectrometer (MC-ICP-MS) using peak hopping of ^(230)Th and ^(229)Th on the central SEM, with either ^(232)Th, ^(236)U (or both) used to monitor for beam intensity. We used in-house laboratory standards to check for machine reproducibility, and the GEOTRACES intercalibration standard to check for accuracy. Over a 1-y period, the 2 s.d. reproducibility on the GEOTRACES SW STD 2010-1 was 2.5% for ^(230)Th, 1.8% for ^(232)Th, and 4% for ^(231)Pa. The lessons learned during this intercalibration process will be of value to those analyzing U-Th-Pa and rare earth elements as part of the GEOTRACES program as well as those using U-series elements in other applications that require high yields and low blanks, such as geochronology

The vanadium isotope composition of Mars: Implications for planetary differentiation in the early solar system

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nielsen, S. G., Bekaert, D., V., Magna, T., Mezger, K., & Auro, M. The vanadium isotope composition of Mars: Implications for planetary differentiation in the early solar system. Geochemical Perspectives Letters, 15, (2020): 35-39, doi:10.7185/geochemlet.2032.The V isotope composition of martian meteorites reveals that Bulk Silicate Mars (BSM) is characterised by δ51V = −1.026 ± 0.029 ‰ (2 s.e.) and is thus ∼0.06 ‰ heavier than chondrites and ∼0.17 ‰ lighter than Bulk Silicate Earth (BSE). Based on the invariant V isotope compositions of all chondrite groups, the heavier V isotope compositions of BSE and BSM relative to chondrites are unlikely to originate from mass independent isotope effects or evaporation/condensation processes in the early Solar System. These differences are best accounted for by mass dependent fractionation during core formation. Assuming that bulk Earth and Mars both have a chondritic V isotopic compostion, mass balance considerations reveal V isotope fractionation factors Δ51Vcore-mantle as substantial as −0.6 ‰ for both planets. This suggests that V isotope systematics in terrestrial and extraterrestrial rocks potentially constitutes a powerful new tracer of planetary differentiation processes accross the Solar System.This work was funded by NASA Emerging Worlds grant NNX16AD36G to SGN. Samples were acquired with funds from the Helmholtz Association through the research alliance HA 203 “Planetary Evolution and Life” to KM. TM contributed through the Strategic Research Plan of the Czech Geological Survey (DKRVO/ČGS 2018-2022). KM acknowledges support through NCCR PlanetS supported by the Swiss National Science Foundation. We thank Jurek Blusztajn for support in the WHOI Plasma Facility

Sources of dehydration fluids underneath the Kamchatka arc

© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Shu, Y., Nielsen, S. G., Le Roux, V., Wörner, G., Blusztajn, J., & Auro, M. Sources of dehydration fluids underneath the Kamchatka arc. Nature Communications, 13(1), (2022): 4467, https://doi.org/10.1038/s41467-022-32211-5.Fluids mediate the transport of subducted slab material and play a crucial role in the generation of arc magmas. However, the source of subduction-derived fluids remains debated. The Kamchatka arc is an ideal subduction zone to identify the source of fluids because the arc magmas are comparably mafic, their source appears to be essentially free of subducted sediment-derived components, and subducted Hawaii-Emperor Seamount Chain (HESC) is thought to contribute a substantial fluid flux to the Kamchatka magmas. Here we show that Tl isotope ratios are unique tracers of HESC contribution to Kamchatka arc magma sources. In conjunction with trace element ratios and literature data, we trace the progressive dehydration and melting of subducted HESC across the Kamchatka arc. In succession, serpentine (250 km depth) break down and produce fluids that contribute to arc magmatism at the Eastern Volcanic Front (EVF), Central Kamchatka Depression (CKD), and Sredinny Ridge (SR), respectively. However, given the Tl-poor nature of serpentine and lawsonite fluids, simultaneous melting of subducted HESC is required to explain the HESC-like Tl isotope signatures observed in EVF and CKD lavas. In the absence of eclogitic crust melting processes in this region of the Kamchatka arc, we propose that progressive dehydration and melting of a HESC-dominated mélange offers the most compelling interpretation of the combined isotope and trace element data.This study was financially supported by grants from the National Natural Science Foundation of China (NSFC) (Grant No. 41903008) and Chinese Postdoctoral Science Foundation (Grant No. 2019M660153) to Y.S., NSF (Grant No. EAR-1829546) to S.G.N. and NSF (Grant No. EAR-1855302) to V.L.R

Size-fractionated major particle composition and concentrations from the US GEOTRACES North Atlantic Zonal Transect

AbstractThe concentration and the major phase composition (particulate organic matter, CaCO3, opal, lithogenic matter, and iron and manganese oxyhydroxides) of marine particles is thought to determine the scavenging removal of particle-reactive TEIs. Particles are also the vector for transferring carbon from the atmosphere to the deep ocean via the biological carbon pump, and their composition may determine the efficiency and strength of this transfer. Here, we present the first full ocean depth section of size-fractionated (1–51µm, >51µm) suspended particulate matter (SPM) concentration and major phase composition from the US GEOTRACES North Atlantic Zonal Transect between Woods Hole, MA and Lisbon, Portugal conducted in 2010 and 2011. Several major particle features are notable in the section: intense benthic nepheloid layers were observed in the western North American margin with concentrations of SPM of up to 1648µg/L, two to three orders of magnitude higher than surrounding waters, that were dominated by lithogenic material. A more moderate benthic nepheloid layer was also observed in the eastern Mauritanian margin (44µg/L) that had a lower lithogenic content and, notably, significant concentrations of iron and manganese oxyhydroxides (2.5% each). An intermediate nepheloid layer reaching 102µg/L, an order of magnitude above surrounding waters, was observed associated with the Mediterranean Outflow. Finally, there was a factor of two enhancement in SPM at the TAG hydrothermal plume due almost entirely to the addition of iron oxyhydroxides from the hydrothermal vent. We observe correlations between POC and CaCO3 in large (>51µm) particles in the upper 2000m, but not deeper than 2000m, and no correlations between POC and CaCO3 at any depth in small (<51µm) particles. There were also no correlations between POC and lithogenic material in large particles. Overall, there were very large uncertainties associated with all regression coefficients for mineral ballast (“carrying coefficients”), suggesting that mineral ballast was not a strong predictor for POC in this section

Nucleosynthetic vanadium isotope heterogeneity of the early solar system recorded in chondritic meteorites

Author Posting. © The Author(s), 2018. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 505 (2019): 131-140, doi:10.1016/j.epsl.2018.10.029.Vanadium (V) isotopes have been hypothesized to record irradiation processes in the early solar system through production of the minor 50V isotope. However, because V only possesses two stable isotopes it is difficult to distinguish irradiation from other processes such as stable isotope fractionation and nucleosynthetic heterogeneity that could also cause V isotope variation. Here we perform the first detailed investigation of V isotopes in ordinary and carbonaceous chondrites to investigate the origin of any variation. We also perform a three-laboratory inter-calibration for chondrites, which confirms that the different chemical separation protocols do not induce V isotope analytical artifacts as long as samples are measured using medium resolution multiple collector inductively coupled plasma mass spectrometry (MCICPMS). Vanadium isotope compositions (51V/50V) of carbonaceous chondrites correlate with previously reported nucleosynthetically derived excesses in 54Cr. Both 51V and 54Cr are the most neutron-rich of their respective elements, which may suggest that pre-solar grains rich in r-process isotopes is the primary cause of the V-Cr isotope correlation. Vanadium isotope ratios of ordinary chondrite groups and Earth form a weaker correlation with 54Cr that has a different slope than observed for carbonaceous chondrites. The offset between carbonaceous and non-carbonaceous meteorites in V-Cr isotope space is similar to differences also reported for chromium, titanium, oxygen, molybdenum and ruthenium isotopes, which has been inferred to reflect the presence in the early solar system of two physically separated reservoirs. The V isotope composition of Earth is heavier than any meteorite measured to date. Therefore, V isotopes support models of Earth accretion in which a significant portion of Earth was formed from material that is not present in our meteorite collections.This study was funded by NASA Emerging Worlds grant NNX16AD36G to SGN

Thallium isotopes as tracers of recycled materials in subduction zones : review and new data for lavas from Tonga-Kermadec and Central America

© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Journal of Volcanology and Geothermal Research 339 (2017): 23-40, doi:10.1016/j.jvolgeores.2017.04.024.Sediment is actively being subducted in every convergent margin worldwide. Yet, geochemical data for arc lavas from several subduction zones, such as Northern Tonga and Costa Rica have revealed either attenuated or limited evidence for sediment in their mantle source regions. Here we use thallium (Tl) isotopes to trace slab components in lavas from the Tonga-Kermadec and Central American arcs. In general, both arcs display Tl isotope data that are most compatible with addition of sediment to the sub-arc mantle from the subducting slab. This evidence is particular strong in the Tonga-Kermadec arc where pelagic clays dominate the Tl budget along the entire arc. Contributions from altered oceanic crust as well as the Louisville Seamount chain that subducts underneath Northern Tonga are not visible in Tl isotopes, which is likely due to the very high Tl concentrations found in pelagic sediments outboard of the Tonga-Kermadec arc. Lavas from Central America reveal variable and systematic Tl isotope compositions along-strike. In particular, lavas from Nicaragua are dominated by contributions from sediments, whereas Costa Rican samples reveal a significant altered oceanic crust component with little influence from sediments on thallium isotope composition. The absence of a sediment signature in Costa Rica corresponds with the Cocos Ridge and the seamount province subduction, which results in a thinner sediment cover. Furthermore, the subducted sediment is dominated by carbonates with very low Tl concentrations and, therefore, small amounts of carbonate sediment added to the mantle wedge do not contribute significantly to the overall Tl budget. A review of Tl isotope and concentration data from the Aleutians, Marianas, Tonga-Kermadec and Central American arcs demonstrate that pelagic sediments are detectable in most arcs, whereas altered oceanic crust components only become appreciable when sediment Tl concentrations are very low (e.g. carbonate) or if sediments are no longer a significant component of the subducting slab (e.g. slab melting in Western Aleutians). As such, Tl isotopes are a promising tool to trace sediment subduction although this requires at least some pelagic sediment is present in the subducted sediment package. We suggest that thallium partitioning between the slab and mantle wedge is most likely controlled by retention in phengite or by partitioning into fluids. Residual phengite likely produces high Cs/Tl ratios because Tl should be more compatible in phengite than is Cs, however, this conclusion needs experimental verification. The stability of phengite is lower at higher fluid contents, which results in hyperbolic relationships between Cs/Tl and possible indicators of fluids such as Sr/Nd and Ba/Th. Thus, combined Tl isotopic and elemental systematics not only provide detailed information about the specific slab components that contribute to arc lavas, but also potentially shed light on the mineralogy and physical conditions of subducting slabs.We gratefully acknowledge funding from NSF grants EAR-1119373 and EAR-1427310 to SGN

Tracking along-arc sediment inputs to the Aleutian arc using thallium isotopes.

Sediment transport from the subducted slab to the mantle wedge is an important process in understanding the chemical and physical conditions of arc magma generation. The Aleutian arc offers an excellent opportunity to study sediment transport processes because the subducted sediment flux varies systematically along strike (Kelemen et al., 2003) and many lavas exhibit unambiguous signatures of sediment addition to the sub-arc mantle (Morris et al., 1990). However, the exact sediment contribution to Aleutian lavas and how these sediments are transported from the slab to the surface are still debated. Thallium (Tl) isotope ratios have great potential to distinguish sediment fluxes in subduction zones because pelagic sediments and low-temperature altered oceanic crust are highly enriched in Tl and display heavy and light Tl isotope compositions, respectively, compared with the upper mantle and continental crust. Here, we investigate the Tl isotope composition of lavas covering almost the entire Aleutian arc a well as sediments outboard of both the eastern (DSDP Sites 178 and 183) and central (ODP Hole 886C) portions of the arc. Sediment Tl isotope compositions change systematically from lighter in the Eastern to heavier in the Central Aleutians reflecting a larger proportion of pelagic sediments when distal from the North American continent. Lavas in the Eastern and Central Aleutians mirror this systematic change to heavier Tl isotope compositions to the west, which shows that the subducted sediment composition is directly translated to the arc east of Kanaga Island. Moreover, quantitative mixing models of Tl and Pb, Sr and Nd isotopes reveal that bulk sediment transfer of ∼0.6–1.0% by weight in the Eastern Aleutians and ∼0.2–0.6% by weight in the Central Aleutians can account for all four isotope systems. Bulk mixing models, however, require that fractionation of trace element ratios like Ce/Pb, Cs/Tl, and Sr/Nd in the Central and Eastern Aleutians occurs after the sediment component was mixed with the mantle wedge. Models of Sr and Nd isotopes that involve sediment melting require either high degrees of sediment melting (>50%), in which case trace element ratios like Ce/Pb, Cs/Tl, and Sr/Nd of Aleutian lavas need to be produced after mixing with the mantle, or significant fluid additions from the underlying oceanic crust with Sr and Nd isotope compositions indistinguishable from the mantle wedge as well as high Sr/Nd ratios similar to that of low (<20%) degree sediment melts. Thallium isotope data from Western Aleutian lavas exhibit compositions slightly lighter than the upper mantle, which implies a negligible sediment flux at this location and probably involvement of low-temperature altered oceanic crust in the generation of these lavas. In general, the lightest Tl isotope compositions are observed for the highest Sr/Y ratios and most unradiogenic Sr and Pb isotope compositions, which is broadly consistent with derivation of these lavas via melting of eclogitized altered oceanic crust

Neodymium isotopes and concentrations in aragonitic scleractinian cold-water coral skeletons - Modern calibration and evaluation of palaeo-applications

TvdF and TS acknowledge financial support for a bursary by the Grantham Institute of Climate Change and the Environment and a Marie Curie Reintegration grant (IRG 230828), as well as funding from the Leverhulme Trust (RPG-398) and the NERC (NE/N001141/1). Additional financial support was provided to LFR by the USGS-WHOI Co-operative agreement, NSF-ANT grants 0636787 and 80295700, The European Research Council, the Leverhulme Trust and a Marie Curie Reintegration grant. LB was supported by a NOAA/UCAR Climate and Global Change Postdoctoral Fellowship and KJM acknowledges funding from a Marie Curie International Outgoing fellowship (IOF 236962).Cold-water corals (CWCs) are unique archives of mid-depth ocean chemistry and have been used successfully to reconstruct the neodymium (Nd) isotopic composition of seawater from a number of species. High and variable Nd concentrations in fossil corals however pose the question as to how Nd is incorporated into their skeletons. We here present new results on modern specimens of Desmophyllum dianthus, Balanophyllia malouinensis, and Flabellum curvatum, collected from the Drake Passage, and Madrepora oculata, collected from the North Atlantic. All modern individuals were either collected alive or uranium-series dated to be < 500 years old for comparison with local surface sediments and seawater profiles. Modern coral Nd isotopic compositions generally agree with ambient seawater values, which in turn are consistent with previously published seawater analyses, supporting small vertical and lateral Nd isotope gradients in modern Drake Passage waters. Two Balanophyllia malouinensis specimens collected live however deviate by up to 0.6 epsilon units from ambient seawater. We therefore recommend that this species should be treated with caution for the reconstruction of past seawater Nd isotopic compositions. Seventy fossil Drake Passage CWCs were furthermore analysed for their Nd concentrations, revealing a large range from 7.3 to 964.5 ng/g. Samples of the species D. dianthus and Caryophyllia spp. show minor covariation of Nd with 232Th content, utilised to monitor contaminant phases in cleaned coral aragonite. Strong covariations between Nd and Th concentrations are however observed in the species B. malouinensis and G. antarctica. In order to better constrain the source and nature of Nd in the cleaned aragonitic skeletons, a subset of sixteen corals was investigated for its rare earth element (REE) content, as well as major and trace element geochemistry. Our new data provide supporting evidence that the applied cleaning protocol efficiently removes contaminant lithogenic and ferromanganese oxyhydroxide phases. Mass balance calculations and seawater-like REE patterns rule out lithogenic and ferromanganese oxyhydroxide phases as a major contributor to elevated Nd concentrations in coral aragonite. Based on mass balance considerations, geochemical evidence, and previously published independent work by solid-state nuclear magnetic resonance (NMR) spectroscopy, we suggest authigenic phosphate phases as a significant carrier of skeletal Nd. Such a carrier phase could explain sporadic appearance of high Nd concentrations in corals and would be coupled with seawater-derived Nd isotopic compositions, lending further confidence to the application of Nd isotopes as a water mass proxy in CWCs.Publisher PDFPeer reviewe

Neodymium isotope analyses after combined extraction of actinide and lanthanide elements from seawater and deep-sea coral aragonite

Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 17 (2016): 232–240, doi:10.1002/2015GC006130.Isotopes of the actinide elements protactinium (Pa), thorium (Th), and uranium (U), and the lanthanide element neodymium (Nd) are often used as complementary tracers of modern and past oceanic processes. The extraction of such elements from low abundance matrices, such as seawater and carbonate, is however labor-intensive and requires significant amounts of sample material. We here present a combined method for the extraction of Pa, Th, and Nd from 5 to 10 L seawater samples, and of U, Th, and Nd from <1 g carbonate samples. Neodymium is collected in the respective wash fractions of Pa-Th and U-Th anion exchange chromatographies. Regardless of the original sample matrix, Nd is extracted during a two-stage ion chromatography, followed by thermal ionization mass spectrometry (TIMS) analysis as NdO+. Using this combined procedure, we obtained results for Nd isotopic compositions on two GEOTRACES consensus samples from Bermuda Atlantic Time Series (BATS), which are within error identical to results for separately sampled and processed dedicated Nd samples (εNd = −9.20 ± 0.21 and −13.11 ± 0.21 for 15 and 2000 m water depths, respectively; intercalibration results from 14 laboratories: εNd = −9.19 ± 0.57 and −13.14 ± 0.57). Furthermore, Nd isotope results for an in-house coral reference material are identical within analytical uncertainty for dedicated Nd chemistry and after collection of Nd from U-Th anion exchange chromatography. Our procedure does not require major adaptations to independently used ion exchange chromatographies for U-Pa-Th and Nd, and can hence be readily implemented for a wide range of applications.Funding that supported this work was received from the National Science Foundation (NSF 0752402), the Leverhulme Trust (RPG-398), the Natural Environmental Research Council (NE/J021636/1 and NE/N003861/1), the European Research Council (278705), and the Grantham Institute for Climate Change.2016-07-0